In a statement to parliament, Foreign and Commonwealth Office Minister David Lidington said the department knew the files had been returned to Britain from former colonies but did not know what had happened to them subsequently.

"It remains the case that the FCO is still unable to confirm the existence or destruction of 170 boxes of top secret colonial administration files known to have been returned to the UK," Lidington said.

"There is some evidence that the Singapore top secret colonial administration files were destroyed as part of a review of FCO post files in the 1990s.

"The FCO continues to search for these files or for further evidence of their destruction."

The acknowledgement came as files relating to controversial British activities in Kenya and Cyprus were made available to the public at The National Archives in southwest London.